Identification of Sequential IgE-Binding Epitopes on Bovine Alpha s2-Casein in Cow’s Milk Allergic Patients

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Identification of Sequential IgE-Binding Epitopes on Bovine Alpha s2-Casein in Cow’s Milk Allergic Patients (1)

Cow’s milk allergy (CMA) is one of the major causes of allergy in childhood. Cow’s milk (CM) has about 30–35 g of proteins per liter, of which 80% are comprised of caseins, and the remaining 20%, of whey proteins. The four casein fractions, alpha s1-, alpha s2-, beta-, and kappa -casein, comprise 32, 10, 28 and 10% of the total milk proteins, respectively. Alpha s2-Casein (25.2 kD) is comprised of 207 amino acids (AA) and has one disulfide bond per molecule. Four genetic variants are known: A, B, C, D. Variants A and D are the most common types observed in European breeds.

Ten IgE-binding regions could be identified; the cumulative ODs for the total study population are shown. 4 of them were recognized by the majority of patients.

With the identification of 10 IgE-binding regions in alpha s2-casein, this report completes the B-cell epitope mapping of the major milk proteins. 2 of the major IgE-binding regions (AA 83–100 and AA 165– 188) share 50% AA sequence homology. The second major IgE-binding region (AA 143–158) contains a phosphorylation site at its amino terminal portion, which may increase its allergenicity. Another phosphorylation site is at AA 168. Dephosphorylation or a natural deletion of a multi-phosphorylation site that occurs in the D variant (AA 51–59) has been shown to significantly diminish the allergenicity of alpha s2-casein.

1. P. J. Busse, K.-M. Järvinen, L. Vila, K. Beyer, H. A. Sampson, Identification of sequential IgE-binding epitopes on bovine αs2-casein in cow’s milk allergic patients. Int. Arch. Allergy Immunol. 129, 93–96 (2002).

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